In process and/or automation engineering, many different field devices are used to determine and/or monitor at least one process variable. These are, for example, fill-level measuring devices, flow meters, pressure and temperature measuring devices, pH-redox potential meters, conductivity meters, etc., which are used for recording the respective process variables, such as fill-level, flow, pressure, temperature, pH level, and conductivity. A field device typically includes at least one sensor unit that at least partially and at least temporarily comes into contact with the process, as well as an electronics unit which, for example, serves to detect, evaluate, and/or supply signals. In the context of the present application, all measuring devices are, in principle, termed field devices, which are used in proximity with the process, and supply or process process-relevant information, i.e., including remote I/O's, wireless adapters, and digital electronic components which are located on the field level.
Flow-measuring devices are, in particular, Coriolis, ultrasound, vortex, thermal, and/or magnetically-inductive flow-measuring devices.
Level-measuring devices are, in particular, microwave level-measuring devices, ultrasonic level-measuring devices, time-domain reflectometry-measuring devices (TDR), radiometric level-measuring devices, capacitive level-measuring devices, conductive level-measuring devices and/or temperature-sensitive level-measuring devices.
Pressure-measuring devices are, in particular, absolute, relative, or differential-pressure devices.
Temperature-measuring devices are, in particular, measuring devices with thermocouples and temperature-dependent resistors.
Limit level-measuring devices are, in particular, vibronic limit level-measuring devices, ultrasonic limit level-measuring devices, and/or capacitive or conductive limit level-measuring devices.
Analytical measuring devices are, in particular, pH sensors, conductivity sensors, oxygen and active oxygen sensors, (spectro)photometric sensors, and/or ion-selective electrodes.
To display information, operating states, measured values, device parameters, etc., field devices frequently have at least one display unit such as a display, or at least one visual and/or acoustic display element. An optical display element is a light-emitting element in particular, an LED. An acoustic element is, for example, a beeper.
The use of individual visual or acoustic display elements proves advantageous with regard to the required space, power consumption of the respective field device, and/or when the field device is used in a potentially explosive environment, such as is the case, for example, with encapsulated field devices that satisfy the IP69K standard. However, the bandwidth of display options is restricted to switching states, operating states, and/or the presence of faults or malfunctions.
DE102006016381A1 describes, for example, a field device with a display unit that comprises at least one LED. DE102008037194A1 describes a field device with a housing, within which a display device is arranged, that, for example, comprises at least one LED for displaying the function or a state of a wireless communications unit.
In addition to a fixed integration of such a display element in an existing field device, the use of subsequently attachable plugs is also known. For this, M12 plugs are frequently used in process and/or automation engineering. However, they are incapable of displaying faults or malfunctions of the field device locally (i.e., at the location of installation in the process). To expand the display options of corresponding display modules, the as yet unpublished German patent application with file number 102013108532.6 describes a plug with at least four display elements, wherein a first display element signals the readiness for operation of the field device, wherein a second and a third display element signal two antivalent switching outputs of the field device, wherein a fourth display element signals a fault or malfunction of the field device, wherein a circuit is provided which is designed such that a fault or malfunction of the field device is recognized using the antivalent switching outputs of the field device, and when a fault or malfunction is recognized, the fourth display element is activated.
Corresponding optical display elements are, for example, frequently also used for vibronic fill-level-measuring devices, such as are produced and marketed by the applicant under the designations LIQUIPHANT and SOLIPHANT, and by means of which a given fill-level is detected. Such field devices frequently also designated limit level switches are preferably used as dry-running protection for pumps, or as an overfill safeguard. The respective switching state is output by a switching output of the field device that is configured according to the type of use. In this context, this is also referred to as MIN-MAX safety. The on-site information concerning the respective switching output or switching state of the limit-level switch is generally very important for a customer, so that display elements with at least one light-emitting element are frequently integrated in the field device, which can at least visualize the respective switching state and/or the operating voltage.
The disadvantage of such display elements in the form of light-emitting elements is, however, that they are frequently difficult to see from a great distance or when the viewing angle is not perpendicular. Consequently, a display module is described in previously unpublished German patent application with file number 102013113438.6 that has a deflection body, such as a light guide, which deflects the light exiting at least one light-emitting element.